$\"\"$

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(a)

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The expression is $\"\"$ .

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Apply formula: $\"\"$

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$\"\"$

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Substitute the values : $\"\"$ . $\"\"$

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$\"\"$ (Simplify)

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$\"\"$ .

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$\"\"$

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(b)

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The expression is $\"\"$ .

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Substitute the values : $\"\"$ .

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$\"\"$

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$\"\"$ (Simplify)

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$\"\"$ .

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$\"\"$

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(a) The exact value of the expression is 0.2588.

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(b) The exact value of the expression is 0.2071.